But, says SAM Principal Investigator Paul Mahaffy of NASA's Goddard Space Flight Center, "We have no definitive detection of Martian organics at this point, but we will keep looking in the diverse environments of Gale Crater."

The sample turned out to be composed of about half common volcanic minerals and half non-crystalline materials such as glass. The water seen by SAM doesn't mean the drift was wet: water molecules bound to grains of sand or dust aren't unusual, although there was more of it in the sample than the researchers had expected.

More excitingly, SAM also tentatively identified the oxygen and chlorine compound perchlorate - a reactive chemical previously found in arctic Martian soil by NASA's Phoenix Lander.

When the sample was heated in SAM, it formed chlorinated methane compounds - one-carbon organics. But while the chlorine is clearly of Martian origin, the researchers say it's possible that the carbon actually originated on Earth, carried there by Curiosity itself.

It's a disappointing finding, especially given the rumors flying about over the last couple of weeks that the rover had actually identified complex organics. But it's early days yet.

"We used almost every part of our science payload examining this drift," says Curiosity project scientist John Grotzinger of the California Institute of Technology in Pasadena.

"The synergies of the instruments and richness of the data sets give us great promise for using them at the mission's main science destination on Mount Sharp."